Many prior art shaft seals have a sealing lip lined with a resin such as e.g., polytetrafluoroethylene. Methods are known for molding an annular lip type shaft seal of the type having an elastomeric body or seal element with a resin liner integrally molded therewith and bonded thereto. These methods include placing a resin washer, an elastomeric preform, and a metal shell in a mold and closing the mold. See, for example, Japanese patent publication Sho 46-23681 announced July 7, 1971 in the Japanese Patent Agency Patent Gazette.
Dual lip shaft seals are known to the art. Conventional dual lip seals have not been previously made with both lips lined during molding with polytetrafluoroehtylene using a single polytetrafluoroethylene disc. Because of the inner (holecut) diameter of the metal support shell and the mold configuration, the polytetrafluoroethylene disc was restricted from reforming downward into the secondary lip approach surface.
The unlined, secondary lip on conventional dual lip seals tended to quickly wear away to shaft size, and this worn secondary lip then became ineffective in protecting the primary lip and stabilizing the sealing element.